We propose to develop non-infectious virion-like particles (VLPs) of HIV-1 that can be used as a vaccination tool for the induction of a broad anti-viral immune response directed against all the major viral accessory proteins of HIV-1. Inactivated virion particles act as immunogens that can be utilized to induce therapeutic immunity. However, wild type virions of HIV-1 cannot be used to mount an immune response against HIV-1 accessory proteins, as they are either absent or present only in trace amounts in the particles. To overcome this limitation, particles will be engineered to contain high amounts of accessory proteins of HIV-1. To this end, HIV-1 Gag which is alone sufficient to drive the formation of virion particles will be fused at its C-terminus to the three early viral gene products Tat, Rev and Nef in a single fusion polyprotein. Four other viral proteins, Vpr, Vif, Vpu and Pol will be incorporated in trans into virion particles, using the ability of Vpr and of Vpr-fusion proteins to bind Gag and to be incorporated in high amounts into particles. This strategy will result in the production of non-infectious virion-like particles (VLPs) containing high amounts of Gag with all the major accessory proteins of HIV. To prove that modified VLPs can induce cellular immune responses directed against structural and accessory proteins of HIV-1 alike; VLPs will be used onto dendritic cells for presentation of VLP-derived epitopes to helper and cytotoxic T cells ex vivo. If the project is successfully completed, modified VLPs could be used alone or in combination with other strategies for vaccination against HIV-1.